A solenoid valve of this kind is known from DE-OS 33 34 158. Similar solenoid valves are also known from DE-OS 33 34 159 and from DE-OS 33 34 160.
In these known solenoid valves the valve member has an approximately T-shaped form with a central limb and two lateral arms. The limb is provided at both sides with a yielding, preferably resilient, closing element which, depending on the state of excitation of the electromagnet which actuates the valve member, selectively closes off one of two valve openings of the valve housing which are arranged on opposite sides of the limb, are spaced from and face one another. Each valve opening communicates with a lateral opening which opens beneath a respective arm of the T-shaped valve member and the transmission members which form the compensation means.
If it is assumed that the limb of the valve member closes one of the valve openings then the pressure at this opening exerts a first turning moment on the valve member. Since this opening communicates with a lateral opening, arranged beneath the arm of the valve member arranged on the same side of the tilt axis in the same pressure as acts at the closed valve opening, brings about a tilting moment on the valve member which opposes the first turning moment. Through corresponding layout of the lever arm and of the opening cross-sections one succeeds in making the two tilting moments of the same size so that they cancel one another. In this state, the other valve opening is open. However, corresponding conditions prevail at this side of the valve member so that the two tilting moments also essentially cancel one another here.
The limb is located in a communication space between the two oppositely disposed valve openings, with this communicating space belonging to the valve passage. This means, that in this embodiment the flow passage extends from the inlet of the valve to the first valve opening, through the ring space and through the second valve opening to the outlet of the valve. If the valve member is moved out of the closed position in which the first valve opening is closed while the second valve opening is opened into a middle position in which the valve member neither closes the first opening, nor the second opening then a flow through the valve is possible. It is also possible to generate a further connection from the outside to the ring space. In this way a 3/2-way valve is provided. The possibility also exists of allowing the second valve opening to be closed by the limb. In this case a communication is present between the inlet side of the valve and the ring space, or a consumer connected to this ring space, a communication to the consumer attached to the outlet of the valve is however interrupted.
The advantage of an arrangement of this kind lies in particular in the fact that the actuating force which is required to tilt the valve member from one switching position to the other switching position is largely independent of the operating pressures since the pressures which prevail in operation always lead to tilting moments which are compensated for. Thus the actuation means essentially only has to overcome friction and to supply the deformation work for the membrane that is used. The actuating force can thus be kept very small, which leads to a compact construction of the electromagnet (solenoid).
In the apparatus known from DE-OS 33 34 158 the transmission members are formed as cylindrical pins which slide in lateral bores and extend through respective ring seals so that the pressures prevailing in the respective bores are transmitted to the arms of the T-shaped valve member. Somewhat problematic with this arrangement is the fact that the frictional effect between the bore and the pins can have disadvantageous effects with the level of the friction which arises changing in operation, for example as a result of mechanical wear on the one hand and jamming on the other hand, and the fact that the seals that are used can lead in the course of time to leakages. The proposal is admittedly contained in DE-OS 33 34 158 that the pistons, i.e. the pins which represent the transfer members of the compensation means can also be replaced by bellows or membrane systems, i.e. when seal friction is undesirable. Nevertheless, the construction of all of the solenoid valves named in the three documents is relatively complicated and problems also arise in that the valve housing has to be split into two and indeed about a central longitudinal axis so that costly manufacturing processes have to be used in order to achieve a good seal between these two housing halves. This two-part construction is however necessary in the named documents in order to ensure precise machining of the valve openings which face one another.